$ cat /etc/X11/gdm/gdm.conf | grep -v ^# | grep -v ^$
[daemon]
AutomaticLoginEnable=false
AutomaticLogin=peter
TimedLoginEnable=true
TimedLogin=peter
TimedLoginDelay=5
Greeter=/usr/bin/gdmlogin
DefaultPath=/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin
RootPath=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/usr/X11R6/bin
User=gdm
Group=gdm
LogDir=/var/log/gdm
PidFile=/var/run/gdm.pid
PostLoginScriptDir=/etc/X11/gdm/PostLogin/
PreSessionScriptDir=/etc/X11/gdm/PreSession/
PostSessionScriptDir=/etc/X11/gdm/PostSession/
DisplayInitDir=/etc/X11/gdm/Init
XKeepsCrashing=/etc/X11/gdm/XKeepsCrashing
RebootCommand=/sbin/reboot;/sbin/shutdown -r now;/usr/sbin/shutdown -r now;/usr/bin/reboot
HaltCommand=/sbin/poweroff;/sbin/shutdown -h now;/usr/sbin/shutdown -h now;/usr/bin/poweroff
ServAuthDir=/var/gdm
BaseXsession=/etc/X11/xdm/Xsession
DefaultSession=default.desktop
UserAuthDir=
UserAuthFBDir=/tmp
UserAuthFile=.Xauthority
StandardXServer=/usr/X11R6/bin/X
Xnest=/usr/X11R6/bin/Xnest -audit 0 -name Xnest
DisplayLastLogin=true
SoundProgram=/usr/bin/play
[security]
AllowRoot=true
AllowRemoteRoot=false
AllowRemoteAutoLogin=true
RelaxPermissions=0
CheckDirOwner=true
RetryDelay=5
DisallowTCP=true
[xdmcp]
Enable=false
[gui]
GtkTheme=Clearlooks
AllowGtkThemeChange=true
GtkThemesToAllow=all
MaxIconWidth=128
MaxIconHeight=128
[greeter]
TitleBar=true
ConfigAvailable=true
Browser=true
MinimalUID=500
Logo=/usr/share/pixmaps/gdm.png
Welcome=%n: Only authorized use permitted
RemoteWelcome=%n: Ony authorized use permitted.
BackgroundType=1
BackgroundImage=/home/peter/Pictures/Country Road in Autumn, Nashville, Indiana.bmp
BackgroundColor=#20305a
BackgroundRemoteOnlyColor=false
ShowGnomeFailsafeSession=false
ShowLastSession=true
Use24Clock=true
GraphicalTheme=happygnome-list
GraphicalThemeDir=/usr/share/gdm/themes/
SoundOnLoginFile=/usr/share/sounds/KDE_Window_Open.ogg
[chooser]
HostImageDir=/usr/share/hosts/
Hosts=
Broadcast=true
Multicast=false
[debug]
Enable=false
[servers]
0=Standard
[server-Standard]
name=Standard server
command=/usr/X11R6/bin/X -audit 0
flexible=true
[server-Terminal]
name=Terminal server
command=/usr/X11R6/bin/X -audit 0 -terminate
flexible=false
handled=false
[server-Chooser]
name=Chooser server
command=/usr/X11R6/bin/X -audit 0
flexible=false
chooser=true

$ cat /etc/sysconfig/desktop~
DESKTOP="GNOME"
DISPLAYMANAGER=KDE

$ cat /etc/sysconfig/desktop
DESKTOP="KDE"
DISPLAYMANAGER=GNOME